1. Field of the Invention
The present invention relates to a method and an apparatus of communication for use with audio visual (AV) systems.
2. Description of the Related Art
Conventional methods of communication between audio visual components basically involve having a master device transmit commands (CMD) to a slave device and then request from the latter the result of command processing thereby, as shown in FIG. 1. Thus if the slave device does not terminate its signal processing for some reason, the master device has to ask for a response with a certain period of time. The impasse keeps the bus occupied. In addition, the master and slave devices must have a master and a slave transmission buffer, respectively, and a master reception (GET-ANS) buffer and a slave reception buffer for the purpose of communication therebetween.
FIG. 2 shows a conventional communication method whereby a master device requests the status of a slave device. FIGS. 3a through 3d depict conventional communication methods whereby the master device transmits commands (CMD) to the slave device and requests from the latter the result of command processing. As illustrated, where commands are to be transmitted, there is no fixed transmission sequence for transmitting the packets. This requires the microcomputer program for communication processing to deal flexibly with diverse procedures of communication. This leads to a relatively large number of program steps required, making program preparation inordinately difficult.
FIGS. 4a through 4c show typical methods of communication under the conventional D2B (digital data bus) communication protocol. As depicted, it requires five packets to send a command to a slave device and to request therefrom the result of command processing (GET-ANS). It then takes seven packets to send a command to the slave device, to request the result of command processing therefrom, and to transmit another command thereto if the request is normally acknowledged. When transmitted, the packets carry not only the data that needs to be sent but also the mode involved, the address of the slave device, the address of the transmitting device, and the type of each transmitted packet. The higher the number of packets needed to accommodate such information, the slower the communication speed.
With the conventional communication methods of FIGS. 4a through 4c, an "END" command packet is used to unlock the slave device. That is, one more packet is needed in addition to those dealing with the processing in question. To transmit the "END" command requires actually transmitting as many as 47 bits because the packet head data such as an address also needs to be sent. A locked slave device means one that accepts only locked communication data packets from its master device and rejects the command packets from any other device. To unlock the slave device requires receiving unlock communication data from the master device that the slave device is locked onto. Once unlocked, the slave device may receive data from any device.